> Because Jean Luc Picard is a Federation citizen, and he wouldn't be happy as other than a starship captain.
There are strong hints in Iain M Banks' Culture series that a significant portion of the mission of Contact and Special Circumstances is giving humans with a pathological need for conflict and excitement something to do to keep them happy.
I got that impression most strongly in The Player of Games. (Minor spoiler alert.) The Minds could have sent an avatar or SC agent to destroy The Empire of Azad, but they figured, "Hey, this Gurgeh guy is bored and he's pretty good at strategy games. Let's kill two birds with one stone."
There are strong hints in Iain M Banks' Culture series that a significant portion of the mission of Contact and Special Circumstances is giving humans with a pathological need for conflict and excitement something to do to keep them happy.